Thin Solid Films (v.515, #12)

Plasma/reactor walls interactions in advanced gate etching processes by R. Ramos; G. Cunge; O. Joubert; N. Sadeghi; M. Mori; L. Vallier (4846-4852).
Wafer-to-wafer reproducibility is a major challenge in gate etching processes. Periodic dry cleaning of the reactor in F-based chemistry between wafers is the most common strategy to ensure process repeatability. However X-ray Photoelectron Spectroscopy analysis of the chamber walls show that this cleaning procedure leaves AlF x species on the reactor walls, eventually resulting in process drifts and formation of particles. We have thus investigated a new cleaning/conditioning strategy of plasma etching reactors, in which the chamber walls are coated by a carbon-rich film between each wafer, allowing stable processing conditions and highly anisotropic etching profile to be achieved in advanced gate stacks. Finally, we present a new method (based on the detection of Cl2 by laser absorption) to characterize the reactor walls conditions that could prevent process drifts.
Keywords: Plasma etching; Process drift; Chamber walls cleaning and conditioning; Aluminum fluoride;

It is shown that a three-dimensional plasma sheath lens that forms on biased electrodes interfacing insulators exhibits novel characteristics such as ion focusing on desired locations, controllability of ion flux uniformity, formation of passive surfaces and applicability to plasma diagnostics. The ion flux profile on substrates of different geometry is obtained by three dimensional simulations of potential distribution and ion trajectory, while experiments are realized in electropositive and electronegative DC and ICP discharges.
Keywords: Plasma sheath; Ion focusing; Plasma diagnostics; Ion etching;

Laser-induced fluorescence ion diagnostics in light of plasma processing by R. McWilliams; J.P. Booth; E.A. Hudson; J. Thomas; D. Zimmerman (4860-4863).
A brief overview of non-perturbing light diagnostics is followed by recent examples of process plasma properties measured via laser-induced fluorescence (LIF), optical emission, and absorption spectroscopy. Examples include radical density measurement via absorption and emission spectroscopy. With LIF, examples show properties of ion beam etching sources and ion velocity angle variations in ICP sheaths near a process surface. Because of the wide range of process plasma parameters, appropriate choice of light diagnostics varies.
Keywords: Plasma spectroscopy; Laser-induced fluorescence;

Study of plasma charging-induced white pixel defect increase in CMOS active pixel sensor by Ken Tokashiki; KeunHee Bai; KyeHyun Baek; Yongjin Kim; Gyungjin Min; Changjin Kang; Hanku Cho; Jootae Moon (4864-4868).
Plasma process-induced “white pixel defect” (WPD) of CMOS active pixel sensor (APS) is studied for Si3N4 spacer etch back process by using a magnetically enhanced reactive ion etching (MERIE) system. WPD preferably takes place at the wafer edge region when the magnetized plasma is applied to Si3N4 etch. Plasma charging analysis reveals that the plasma charge-up characteristic is well matching the edge-intensive WPD generation, rather than the UV radiation. Plasma charging on APS transfer gate might lead to a gate leakage, which could play a role in generation of signal noise or WPD. In this article the WPD generation mechanism will be discussed from plasma charging point of view.
Keywords: CMOS APS; white pixel defect; plasma charging damage;

Plasma parameters in the vicinity of the dielectric window of a low density, microwave discharge produced in O2 at 915 MHz are investigated by a spherical probe and optical emission spectroscopy while the microwave field distribution is measured by a spectrum analyzer. The electron energy distribution function is found to be strongly dependent on the position with respect to the slot antenna, exhibiting a group of energetic electrons at locations where the electric field and the optical intensity exhibit maximum values. The density of energetic electrons decreases sharply just a few cm away from the dielectric.
Keywords: Surface wave plasma; Heating mechanism; Langmuir probe; Thermal probe;

Profile simulation of high aspect ratio contact etch by Doosik Kim; Eric A. Hudson; David Cooperberg; Erik Edelberg; Mukund Srinivasan (4874-4878).
A semi-empirical profile simulator was employed to better understand fundamental mechanisms of feature evolution in a high aspect ratio contact plasma etch process. Simulation results showed that the net deposition rate of polymer on sidewall defined the necking and surface scattering of ions from the secondary facet caused the formation of bowing. As neutral depositor flux was increased, the resulting profile showed a monotonic increase in necking. In contrast, the extent of bowing showed a maximum, such that minimal bowing was obtained at low and at high depositor fluxes. Primary faceting of photo resist showed only a small influence on the SiO2 etch profile.
Keywords: Plasma etch; Profile simulation; High aspect ratio contact; Etch profile;

Silicon Dioxide (SiO2) thin film deposition processes were studied with the use of classical Molecular Dynamics (MD) simulations combined with Monte Carlo (MC) simulations. The MC simulations are shown to efficiently emulate thermal relaxation processes during deposition. Dependence of deposited film properties on the incident kinetic energies is examined from the numerical simulations.
Keywords: Molecular Dynamics; Monte Carlo method; SiO2; Deposition;

Angular dependence of sputtering yields of SiO2 substrates subject to CF3 beam injections is evaluated with the use of molecular dynamics simulations. The obtained sputtering yield data are in reasonable agreement with experimental observations. Atomic compositions in the SiO2-CF mixing layer as well as kinetic energies and atomic compositions of sputtered species also exhibit strong dependence of the injection angle.
Keywords: Molecular dynamics simulations; Fluorocarbon; Plasma etching; Plasma surface interaction;

The ion dose non-uniformity induced on the wafer surface by modal and discrete focusing effects is investigated for different plasma densities and implantation parameters. Measured impact radius agrees well with values obtained by simulation. The optical pattern observed on the wafer surface is correlated with the ion dose by FT-IR measurements. The applicability of a previously proposed vertical ring is demonstrated, the ring being able to considerably improve the ion flux uniformity by shifting the discrete focusing effect out of the wafer surface and reducing the modal focusing. Experiments are performed in an inductively coupled plasma produced in hydrogen.
Keywords: Plasma immersion ion implantation; Dose uniformity; Sheath-lens focusing effect; Guard ring;

Threshold voltage shift of submicron p-channel MOSFET due to Si surface damage from plasma etching process by Gwan-Ha Kim; Young-Rog Kang; Whan-Jun Kim; Sang-Yong Kim; Chang-Il Kim (4892-4896).
We compared performances for transistors produced using both wet and dry etching for non-silicide processes in the CMOS technology. It was found that the dry process for non-silicide area induces the threshold voltage shifting of the pMOS transistor as well as increases the contact resistance on active region. Also, GIDL (gate-induced-drain-leakage) current has a poor junction leakage current compared with the wet etching process. Moreover, the dry etching process changes the doping profile of the P+ junction and the p-channel transistor region. The experiments showed the dry etching process generates the Si–SiO2 interface trap site due to plasma-induced damage.
Keywords: Plasma charging damage; Threshold voltage shift; Gate-induced-drain-leakage current;

Control of substrate surface temperature in millisecond annealing technique using thermal plasma jet by T. Okada; S. Higashi; H. Kaku; N. Koba; H. Murakami; S. Miyazaki (4897-4900).
Temporal variations of substrate surface temperature in scanning Ar thermal plasma jet has been investigated based on an analysis of transient changes in optical reflectivity. The accuracy of the temperature measurement has been evaluated to be 30 K at temperature around 1760 K. The maximum surface temperature (T max) is controlled in the range from ∼ 960 to ∼ 1780 K with keeping the annealing duration (t a) around ∼ 3 ms by changing the Ar gas flow rate (f) and distance between the plasma jet and the substrate (d) under a constant scanning speed (ν) of 500 mm/s.
Keywords: Rapid thermal annealing; Temperature measurement; Thermal plasma jet;

Fabrication and characteristics of out-of-plane piezoelectric micro grippers using MEMS processes by Chang-Seong Jeon; Joon-Shik Park; Sang-Yeol Lee; Chan-Woo Moon (4901-4904).
Out-of-plane type piezoelectric micro grippers (briefly, OPPMG) actuated by micro cantilevers using sol–gel multi-coated PZT (Pb(Zr0.52Ti0.48)O3) films with the thickness of 1.2 μm were newly designed and fabricated using MEMS processes. Electromechanical and gripping characteristics of fabricated micro PZT cantilevers and OPPMG using them have been investigated. Two types of micro PZT cantilevers were fabricated with two types of supporting layers, respectively. The OPPMG was formed by two micro PZT cantilevers of the same type facing each other across the spacer of polyimide (PI). Precise gripping and positioning of metallic ball with diameter of 100 μm using fabricated OPPMGs was successfully done at a low actuating voltage of 7 V, without any adhesion problems between two jaws of gripper and the ball.
Keywords: PZT cantilever; Micro gripper; Piezoelectric actuator; MEMS;

The fabrication of mesoporous tungsten oxide films by spin-coating method followed by an atmospheric plasma-calcination method is described and discussed here. For the calcination process the dielectric barrier discharge system generating homogenous atmospheric plasma discharge was designed and used. By this method, large surface area mesoporous films, with disordered pores of average diameter size of about 4 to 5 nm were synthesized. All the plasma-calcined films exhibit amorphous structure. The process of calcination was evaluated by FT-IR spectroscopy and in comparison with other methods a very high speed of calcination process was achieved.
Keywords: Mesoporous tungsten oxide; Spin-coating; Plasma-calcination; Dielectric barrier discharge;

Oxygen and helium gases, often used in many plasma processes, were added to argon-based glow plasmas, produced at the atmospheric pressure, in order to study the controllability of the plasma characteristics by the supply gas mixing. Based on the electrical and optical diagnostics, the plasma parameters, such as the breakdown voltage, the rotational temperature, and the plasma uniformity, and their changes due to the gas mixing were investigated. The experimental results showed that the helium gas addition reduced the breakdown voltage (from 430 V to 300 V), the rotational temperature (from 465 K to 360 K), and the plasma uniformity. On the other hand, a small amount of oxygen gas increased the breakdown voltage (from 435 V to 463 V) and the rotational temperature (from 520 K to 600 K) due to various energy loss channels of the oxygen gas. The experimental results showed that it was possible to control the plasma characteristics by the gas mixing.
Keywords: Gas mixing; Atmospheric plasma; Large area plasma;

A few millimeter size plasma was generated in a pin to plane electrode configuration with either Aluminum or Indium Tin Oxide glass. Depending on the plane electrode material, the plasma showed either corona or corona-dielectric barrier discharge hybrid discharge characteristics. From electrical and optical diagnostics, it was found that the hybrid discharge was more electrically stable and had lower rotational temperature. A feasibility study of material surface modification was performed with the hybrid discharge. All samples such as polyethylene and polypropylene films became more hydrophilic, and the surface property was changed only within the radius of less than about 12 mm. In addition, several effects of gas temperature and treatment time on the surface modification were studied besides the durability.
Keywords: Atmospheric plasma; Corona-DBD hybrid plasma; Surface modification;

A novel deep etching technology for Si and quartz materials by Yasuhiro Morikawa; Tooru Koidesawa; Toshio Hayashi; Koukou Suu (4918-4922).
A disadvantage of ICP type plasma etching method compared with CCP one is low selectivity to photo resist. So a novel etching method was developed to obtain high selectivity to photo resist by incorporating a sputtering method, in which a target was placed on the opposite side of the substrate. Satisfactory results were obtained for a continuous gas feeding treatment and also for a gas modulating treatment.
Keywords: Plasma process and deposition; Etching; NLD plasma; Deep etching; Silicon; Quartz; MEMS;

Etching characteristics and modeling for oval-shaped contact by Sung-Chan Park; Seok-Hyun Lim; Chul-Ho Shin; Gyung-Jin Min; Chang-Jin Kang; Han-Ku Cho; Joo-Tae Moon (4923-4927).
In this study, etching characteristics of oval-shaped contact were investigated. The oval-shaped contact showed different etching characteristics compared to the circular contact. The long axis cross-section of oval-shaped contact showed a more vertical profile and a less bowing compared to the short axis. To explain these phenomena, we simulated ion reflection from sloped oval-shaped hard-mask. From the simulation, we found that the ions reflected from hard-mask accumulated more toward short axis sidewall first. This ion accumulation and asymmetric charging explained the reason behind larger bowing and slopped profile phenomena of short axis.
Keywords: Etching; Oval shape; Simulation; Bowing;

Improvement in gate LWR with plasma curing of ArF photoresists by A. Ando; E. Matsui; N.N. Matsuzawa; Y. Yamaguchi; K. Kugimiya; M. Yoshida; K.M.A. Salam; T. Kusakabe; T. Tatsumi (4928-4932).
The line width roughness (LWR) in gate electrodes is one of the most critical issues in obtaining sufficient transistor performance in 45-nm half-pitch (hp 45) node devices. ArF (argon fluoride) photoresists are, however, very fragile and easily deformed during plasma exposure. We evaluated the change in the chemical nature of an ArF photoresist caused by various plasmas and found that “HBr plasma curing” induces the selective detachment of heterocyclic units in the photoresist. We found that the glass transition temperature (T g) of the photoresist decreased due to this detachment, leading to surface smoothening of the photoresist layer. Finally, we applied this curing process to the fabrication of line patterns and it was demonstrated that the process remarkably improved LWR.
Keywords: LWR; HBr plasma; Lactonyl unit; ArF;

Control of oxidation on NiSi x during etching and ashing processes by S. Sakamori; K. Yonekura; N. Fujiwara; T. Kosaka; M. Ohkuni; K. Tateiwa (4933-4936).
The oxidation on nickel silicide (NiSi x ) during plasma etching and oxygen ashing is investigated for stable contact resistance on NiSi x . NiSi x exposed by various processes is observed by X-ray photoelectron spectroscopy. The oxidation on NiSi x is promoted by the fluorine that remains during etching and the oxide thickness on n + NiSi x is greater than that on p + NiSi x . The remaining fluorine after etching can be decreased by in-situ nitrogen plasma treatment during the post-etching process. Therefore, the oxidation progress with exposure to air and the difference in oxidation on NiSi x between n + and p + can be suppressed.
Keywords: Etching; X-ray photoelectron spectroscopy; Nickel; Oxidation;

Effects of radical-distribution control on etching-profile uniformity in dielectric etching by Hiroyuki Kobayashi; Ken'etsu Yokogawa; Kenji Maeda; Tadamitsu Kanekiyo; Masaru Izawa (4937-4940).
Uniformity control of etching profile and etching rate across a wafer during damascene etching was investigated using a UHF-ECR etching apparatus with a dual-zone gas-injection system. Uniform etching rate was obtained under various conditions by controlling magnetic field distribution. It was found that etching profile could be controlled without affecting etching-rate uniformity by changing the ratio of inner- to outer-nitrogen-gas flow rate above the wafer. The effect of feed-gas control on radical distribution was evaluated by simulation and measurement of the radical distribution, which showed that controlling the gas-mixing ratio changed the distribution of the nitrogen-to-CF x ratio. With SiOC via hole etching, nanometer-level bottom-CD uniformity at high etching-rate uniformity was obtained.
Keywords: Etching; Dielectrics; Damascene; UHF-ECR plasma;

Controlling gate-CD uniformity by means of a CD prediction model and wafer-temperature distribution control by S. Kanno; G. Miya; J. Tanaka; T. Masuda; K. Kuwahara; M. Sakaguchi; A. Makino; T. Tsubone; T. Fujii (4941-4944).
A technique for predicting wafer temperature was developed, and a model for predicting critical dimension (CD) was devised. Using this technique and model in combination makes it possible to calculate wafer temperature during gate etching within an accuracy of 1 °C and to predict CD distribution after plasma etching. Etching at a temperature for uniform CD given by the CD prediction model reduces the CD variation (3σ) during gate etching from 2.3 to 1.5 nm. Applying this temperature prediction technique and CD prediction model together will contribute to improving etching apparatus design and process development.
Keywords: CD prediction model; Wafer temperature; Reaction product; Uniformity;

Chemical dry etching of silicon oxide in F2/Ar remote plasmas by S.C. Kang; D.J. Kim; J.Y. Hwang; Y.B. Yun; N.-E. Lee; Y.C. Jang; G.H. Bae (4945-4949).
In this study, we carried out chemical dry etching of silicon oxide layers by F2/Ar remote plasmas generated from a toroidal-type remote plasma source. Chemical dry etching experiments were performed by varying the F2 gas flow rate, F2/(F2  + Ar) flow ratio, and substrate temperature. Under the current experimental condition, the chemical etching rates were significantly enhanced with increasing the F2 gas flow rate and F2/(F2  + Ar) flow ratio. Observed tendency in the etch rate was consistent with the variations of the optical emission intensity of the F radicals in the afterglow region of the remote plasma source and of the concentration of the emitted SiF4 reaction by-products in the exhaust. The substrate temperature was the most influential process parameter in determining the chemical etching rates. Increasing the substrate temperature enhanced the etching rate by a factor of 2.9 ∼ 4.4 depending on the F2/(F2  + Ar) flow ratio.
Keywords: Chemical dry etching; Remote plasma; Silicon oxide; Fluorine gas;

Effect of doping elements on ZnO etching characteristics with CH4/H2/Ar plasma by M.H. Shin; M.S. Park; S.H. Jung; J.H. Boo; N.-E. Lee (4950-4954).
Effect of doping elements on the etching characteristics of doped-ZnO (Ag, Li, and Al) thin films, etched with a positive photoresist (PR) mask, and an etch process window for infinite etch selectivity were investigated by varying the CH4 flow ratio and self-bias voltage, Vdc, in inductively coupled CH4/H2/Ar plasmas. Increased doping of ZnO films decreased the etch rates significantly presumably due to lower volatility of reaction by-products of doped Li, Ag, and Al in CH4/H2/Ar plasmas. The etch rate of AZO (Al-doped ZnO) was most significantly decreased as the doping concentration is increased from 4 to 10 wt%. It was found that process window for infinite etch selectivity of the doped ZnO to the PR is closely related to a balance between deposition and removal processes of a-C:H (amorphous hydrogenated carbon) layer on the doped-ZnO surface. Measurements of optical emission of the radical species in the plasma and surface binding states by optical emission spectroscopy (OES) and X-ray photoelectron spectroscopy (XPS), respectively, implied that the chemical reaction of CH radicals with Zn atoms in doped-ZnO play an important role in determining the doped-ZnO etch rate together with an ion-enhanced removal mechanism of a-C:H layer as well as Zn(CHx)y etch by-products.
Keywords: Doped-ZnO; Plasma etching; Inductively coupled plasma; XPS; OES;

Magnesium oxide thin film has been widely used as a buffer layer and substrate for growing various thin film materials because of very low Gibbs free energy, low dielectric constant and low refractive index. The investigations of the MgO etching characteristics in BCl3/Ar plasma were carried out using the inductively coupled plasma system. It was found that the increasing BCl3 in the mixing ratio of BCl3/Ar plasma causes monotonic MgO etch rate. The results showed in the BCl3-rich plasma that the etching process is dominantly supplied by the chemical pathway through the ion-assisted chemical reaction.
Keywords: Magnesium oxide; Etching; Inductively coupled plasma; Langmuir probe;

Sacrificial CVD film etch-back process for air-gap Cu interconnects by Shoichi Uno; Kiyomi Katsuyama; Junji Noguchi; Kiyohiko Sato; Takayuki Oshima; Masanori Katsuyama; Kazusato Hara (4960-4965).
A novel sacrificial chemical vapor deposition film etch-back process for Cu air-gap interconnects was developed. The etched-back Cu surfaces were analyzed by X-ray photoelectron spectroscopy. The electrical characteristics and the stress induced voiding reliability were evaluated. The CF4 etch-back process was found not to degrade interconnect reliability. A four-level dual damascene Cu interconnect structure was successfully fabricated, and its effective dielectric constant was 2.8, 32% lower than that of a conventionally fabricated one. In situ N2 or Ar plasma treatments after etch-back were investigated to reduce the Cu degradation.
Keywords: Air-gap; Cu interconnect; Low-k; Plasma treatment;

Suppression of hydrogen-ion drift into underlying layers using plasma deposited silicon oxynitride film during high-density plasma chemical vapor deposition by T. Murata; T. Yamaguchi; M. Sawada; S. Shimizu; K. Asai; K. Kobayashi; H. Miyatake; M. Yoneda (4966-4970).
Hydrogen ions drifting into underlying layers during HDP-CVD were successfully suppressed by the insertion of plasma deposited silicon oxynitride (p-SiO x N y H z ) film, and the hydrogen-trapping mechanism was clarified. The hydrogen ions are trapped in bonding states, not in interstitial ones. After HDP-CVD undoped silicate glass (HDP-USG) film deposition on the p-SiO x N y H z film, the decrease of the dangling bonds in the p-SiO x N y H z film measured by ESR was much lower than the increase of the desorbed hydrogen concentration measured by TDS. These results suggest that new hydrogen-trapping sites are mainly generated from ESR-inactive bonds by drifted hydrogen ions and atomic hydrogen during HDP-CVD.
Keywords: Plasma processing and deposition; Hydrogen; Silicon oxide;

Growth of crystallized Ge films from VHF inductively-coupled plasma of H2-diluted GeH4 by T. Sakata; K. Makihara; H. Murakami; S. Higashi; S. Miyazaki (4971-4974).
We have studied the Ge crystalline nucleation and film growth on quartz substrate at 250 °C from inductively-coupled plasma (ICP) of GeH4 diluted with H2. The ICP was generated by supplying 60 MHz power to an external single-turn antenna which was placed on a quartz plate window of a stainless steel reactor and parallel to the substrate. We have found that the growth rate is significantly increased when the preferential growth of the (110) plane becomes pronounced after the formation of randomly-oriented crystalline network. The (110) oriented Ge films, of which average crystallinity is as high as 70%. The integrated intensity ratio of TO phonons in crystalline phase to those in disordered phase, were grown at a rate of ∼ 4.0 nm/s after the formation of amorphous incubation layer with a thickness of ∼ 0.1 μm on quartz.
Keywords: VHF–ICP; Germanium; Crystallinity; High-rate deposition;

Epitaxial growth of lithium niobate film using metalorganic chemical vapor deposition by Yasunobu Akiyama; Katsuya Shitanaka; Hiroshi Murakami; Young-Sik Shin; Michihide Yoshida; Nobuyuki Imaishi (4975-4979).
Lithium niobate films grown epitaxially on sapphire substrate were prepared using a thermal chemical vapor deposition method from the metalorganic compounds Li(C11H19O2) and Nb(OC2H5)5. The range of operating conditions for obtaining pure epitaxially grown LiNbO3 without other oxides is within that for obtaining pure polycrystalline LiNbO3 grown on silicon substrate. On analyzing the composition of the epitaxially grown LiNbO3 film, the composition of the film was similar to that of the LiNbO3 solid solution in the phase diagram of the Li–Nb composite oxide obtained for crystal growth from a molten solution.
Keywords: Chemical vapor deposition; Epitaxy; Lithium niobate;

Ni-silicide precursor for gate electrodes by M. Ishikawa; I. Muramoto; H. Machida; S. Imai; A. Ogura; Y. Ohshita (4980-4982).
Ni-silicide film was deposited at a low temperature of 160 °C by CVD using a Ni(PF3)4/Si3H8 gas system. Injecting Si3H8 during the Ni deposition does not affect the deposition rate, but the step-coverage quality deteriorates at high growth temperatures. At high growth temperatures, the Ni/Si ratio of the film deposited on the sidewall varies as the distance from the open area increases. High step-coverage quality and a constant Ni/Si ratio independent of the location of the deposition are strongly required to fabricate a three-dimensional device. These requirements were achieved with this CVD by depositing the Ni-silicide film below 180 °C.
Keywords: Ni-silicide; CVD; Ni(PF3)4; Si3H8;

Microcrystalline silicon (μc-Si) and polycrystalline silicon (poly-Si) films are deposited by surface wave (SW) discharge at 2.45 GHz in H2/SiH4 gas. This high density SW plasma at relatively low pressures (4–60 Pa) enables strong dissociation of feedstock gas. The films deposited on substrate are investigated by X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). The SW discharge in 10% SiH4 at total pressure of ∼ 30 Pa gives μc-Si films on a substrate at 250 °C, at a fairly high deposition rate of 4–20 nm/s, with a crystalline volume fraction of 0.5–0.8 and a grain size of 10–40 nm. Furthermore, poly-Si film with crystalline volume fraction of > 99% is deposited at higher substrate temperature (400 °C) in 2% SiH4 discharge at lower pressure (4 Pa). X-ray diffraction and SEM results revealed that the grain size of poly-Si films is as large as 600 nm, which is almost 6 times larger than previously reported values.
Keywords: Plasma CVD; Microcrystalline silicon; Polycrystalline silicon; Surface wave plasma; Grain size;

Improved crystallization characteristics of ZnO thin film grown onto a-C:H film used as a buffer layer by Eung Kwon Kim; Tae Yong Lee; Yong Seob Park; Somnath Ghosh; Byungyou Hong; Young Sung Kim; Joon Tae Song (4988-4991).
We employed a-C:H buffer layer to improve the crystalline property of ZnO thin film for the membrane film bulk acoustic resonator (FBAR). The a-C:H film as a buffer layer is prepared by applying dc bias of 200 V and also this sample showed a smoother surface roughness, higher hardness and Young's modulus when compared to the other samples. In addition, the FWHM value was improved from 7.5 to 4.3° on a-C:H film. The fabricated FBAR device showed the resistivity of 0.73 × 108 Ω when compared with no buffer layer and the frequency characteristics of the FBAR were finally confirmed to be 1.15 GHz and 21.24 dB, respectively.
Keywords: a-C:H film; ZnO thin film; Buffer layer; FBAR;

Single-phase monoclinic vanadium dioxide (VO2) films were grown on a Si(100) substrate using inductively coupled plasma (ICP)-assisted sputtering with an internal coil. The VO2 film exhibited metal-insulator (M-I) transition at around 65 °C with three orders of change in resistivity, with a minimum hysteresis width of 2.2 °C. X-ray diffraction showed structural phase transition (SPT) from monoclinic to tetragonal rutile VO2. For conventional reactive magnetron sputtering, vanadium oxides with excess oxygen (V2O5 and V3O7) could not be eliminated from stoichiometric VO2. Single-phase monoclinic VO2 growths that are densely filled with smaller crystal grains are important for achieving M-I transition with abrupt resistivity change.
Keywords: Metal-insulator phase transition; VO2 film; Resistivity change; Inductively coupled plasma-assisted sputtering;

Sputter deposition followed by surface treatment was studied using reactive RF plasma as a method for preparing titanium oxide (TiO2) films on indium tin oxide (ITO) coated glass substrate for dye-sensitized solar cells (DSCs). Anatase structure TiO2 films deposited by reactive RF magnetron sputtering under the conditions of Ar/O2(5%) mixtures, RF power of 600 W and substrate temperature of 400 °C were surface-treated by inductive coupled plasma (ICP) with Ar/O2 mixtures at substrate temperature of 400 °C, and thus the films were applied to the DSCs. The TiO2 films made on these experimental bases exhibited the BET specific surface area of 95 m2/g, the pore volume of 0.3 cm2/g and the TEM particle size of ∼ 25 nm. The DSCs made of this TiO2 material exhibited an energy conversion efficiency of about 2.25% at 100 mW/cm2 light intensity.
Keywords: TiO2; Sputter deposition; RF magnetron sputtering; Plasma surface treatment; Dye-sensitized solar cell;

Hydrogenated films of silicon nitride (SiNx:H) were investigated by varying the deposition condition in plasma enhanced chemical vapor deposition (PECVD) reactor and annealing condition in infrared (IR) heated belt furnace to find the optimized condition for the application in multicrystalline silicon solar cells. By varying the gas ratio (ammonia to silane), the silicon nitride films of refractive indices 1.85–2.45 were obtained. Despite the poor deposition rate, silicon wafer with the film deposited at 450 °C showed the best minority carrier lifetime. The film deposited with the gases ratio of 0.57 showed the best peak of carrier lifetime at the annealing temperature of 800 °C. The performance parameters of cells fabricated by varying co-firing peak temperature also showed the best values at 800 °C. The multicrystalline silicon (mc-Si) solar cells fabricated in conventional industrial production line applying the optimized film deposition and annealing conditions on large area substrate (125 mm × 125 mm) was found to have the conversion efficiency of 15%.
Keywords: Multicrystalline silicon; Solar cells; Silicon nitride films; PECVD;

Silicon nitride (SiN X ) thin films were deposited by means of an RF plasma enhanced chemical vapor deposition (PECVD) reactor using SiH4 and N2 gases. The refractive index of the SiN thin films increased from 1.5652 to 2.7621 as the SiH4/N2 flow ratio was increased from 0.16 to 1.66, since the amount of Si in the film increased, while that of N decreased, as the SiH4/N2 flow ratio was increased. The core shape became circular after annealing at 1200 °C. This change is related to a decrease in the viscosity with increasing annealing temperature. This decreased viscosity causes condensation of the core layer due to surface tension, which leads to the change in shape from rectangular to circular. The thickness, refractive index and shape of the films were characterized by ellipsometry, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS).
Keywords: Refractive index; Optical waveguide; Silicon nitride; PLC;

Carbon incorporation process in GaAsN films grown by chemical beam epitaxy using MMHy or DMHy as the N source by H. Suzuki; K. Nishimura; H.S. Lee; Y. Ohshita; N. Kojima; M. Yamaguchi (5008-5011).
Crystal quality of GaAsN films can be improved by using CBE for low-temperature growth. However, low-temperature growth increases C incorporation in the films, which degrades their electrical properties. Consequently, C incorporation was investigated in view of the surface reaction of N sources on a substrate surface, and MMHy and DMHy were compared. When MMHy was used as an N source, C concentration in GaAsN drastically increases below 380 °C than that in GaAs due to insufficient CH x desorption. In the case of DMHy, N(CH3)2 is desorbed more readily than CH x , therefore, the C concentration can then be reduced using DMHy.
Keywords: Gallium arsenide nitride; Chemical beam epitaxy; Temperature programmed desorption; Impurities;

Suppression of 193-nm photoresist deformation by H2 addition to fluorocarbon plasma in via-hole etching by Kazumasa Yonekura; Kazunori Yoshikawa; Yuji Fujiwara; Shigenori Sakamori; Nobuo Fujiwara; Takayoshi Kosaka; Mitsuhiro Ohkuni; Kenji Tateiwa (5012-5018).
Suppression of 193-nm photoresist deformation by H2 addition to fluorocarbon plasmas in via-hole etching is investigated for sub-65-nm-node dual-damascene patterning. Photoresist deformation causes profile distortion and results in degradation of reliability, such as the line-to-line time dependent dielectric breakdown. To prevent profile distortion, H2 addition to fluorocarbon plasma is investigated in terms of fluorocarbon polymer and photoresist modification. XPS, FT-IR, and highlight etching investigations reveal that the H2 plasma treatment extracts oxygen from the photoresist and modifies it. This modification suppresses the photoresist deformation and H2 addition to fluorocarbon plasmas can have the same effects as the H2 plasma treatment. Finally, a highly reliable damascene interconnection is successfully achieved.
Keywords: Etching; Plasma processing and deposition; Hydrogen; X-ray photoelectron spectroscopy (XPS);

Novel organosiloxane vapor annealing process for improving properties of porous low-k films by K. Kohmura; H. Tanaka; S. Oike; M. Murakami; N. Fujii; S. Takada; T. Ono; Y. Seino; T. Kikkawa (5019-5024).
A novel 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS)-vapor annealing method was developed for improving the mechanical strength of porous silica films with a low dielectric constant. TMCTS molecules react with Si–OH groups on the pore wall surfaces to form the polymer network which results in the high hydrophobicity and reinforcement of the silica wall. This method can be used to recover plasma damages induced by etching and ashing in fabricating Cu/low-k interconnects.
Keywords: Porous silica film; Dielectric properties; Mechanical properties; Silylation;

Characterization and integration of new porous low-k dielectric (k  < 2.3) for 65 nm technology and beyond by Kyeong-Keun Choi; Ihl Hyun Cho; Sang Jong Park; Jung Eun Lim; Oh Jin Jung; Jong Hyuk Park; Byung Seung Min; Sung Bo Hwang; Min Jin Ko; Jeong Gun Lee (5025-5030).
In this paper, new porous spin-on dielectric (HL02™, trademark of the LG Ltd.) was studied. The characterizations, such as thermal stability, chemical structure, dielectric constant (k) and mechanical properties (hardness and modulus), of methylsilsesquioxane (MSQ)-based dielectrics were evaluated. An optimized material (k  = 2.25), characterized by a hardness and a modulus of 1.0 GPa and 6.5 GPa each in association with a porosity of 30% and a mean pore radius of 2.2 nm, was successfully integrated in damascene process with 10 levels of Cu/low-k film for 65 nm technology and beyond. Good electrical results were obtained in metal line resistance and leakage current.
Keywords: Porous low-k; Copper; Integration; Methylsilsesquioxane (MSQ);

Influences of atomic hydrogen on porous low-k dielectric for 45-nm node by K. Tomioka; E. Soda; N. Kobayashi; M. Takata; S. Uda; K. Ogushi; Y. Yuba; Y. Akasaka (5031-5034).
Atomic hydrogen generated by a heated tungsten catalyzer has been investigated in terms of the damage-less ash and restoration of damaged low-k dielectric. No difference of damaged thickness of low-k dielectric between before and after the ash by HF dip using patterned porous methyl silsesquioxane (MSQ) film was found. Moreover atomic hydrogen exposure slightly reduced capacitance of the micro-structured capacitor with the Cu wire and the CVD porous low-k dielectric.
Keywords: Ash; Low-k; Hydrogen; Catalyzer;

Two structures of low dielectric constant (low-k) SiOC films were elucidated in this work. Low-k thin film by remote plasma mode was mainly composed of inorganic Si–O–Si backbone bonds and some oxygen atoms are partially substituted by CH3, which lowers k value. The host matrix of low-k thin films deposited by direct plasma mode, however, was mainly composed of organic C–C bonds and “M” and “D” moieties of organosilicate building blocks, and thus the low dipole and ionic polarizabilities were the important factors on lowering k value.
Keywords: Low-k; Structure; XPS; FT-IR;

Low dielectric constant SiOC(–H) thin films were deposited by plasma enhanced chemical vapor deposition (PECVD) using methyltriethoxysilane (MTES) and oxygen as precursors. The SiOC(–H) films were prepared with MTES/O2 flow rate ratio of 80%, rf power of 700 W and the working pressure was varied from 110 to 150 mTorr. Then the films were annealed at different temperatures in an Ar ambient for 30 min in order to study their thermal stability. Film thickness and refractive index were measured by SEM and ellipsometry, respectively. Bonding characteristics of the films were investigated by Fourier transform infrared (FTIR) spectroscopy. The dielectric constant of SiOC(–H) film was evaluated by CV measurements using Al/SiOC(–H)/p-Si structure. The dielectric constants as low as 2.4 have been obtained for the film annealed at 500 °C with the working pressure of 150 mTorr. The annealing treatment was found to reduce dielectric constant significantly due to abundant incorporation of methyl group into the Si–O network. These results demonstrated the promising characteristics of SiOC(–H) thin films deposited by using oxygen and MTES precursor.
Keywords: SiOC(―H); PECVD; MTES; Low-k dielectrics;

In this study, the effect of BCl3/C4F8 gas mixture on the ZrO x etch rates and the etch selectivities of ZrO x /Si were investigated and its etch mechanism was studied. The increase of C4F8 in BCl3/C4F8 decreased the silicon etch rate significantly and finally deposition instead of etching occurred by mixing C4F8 more than 3%. In the case of ZrO x , the etch rate remained similar until 4% of C4F8 was mixed, however, the further increase of C4F8 percentage finally decreased the ZrO x etch rate and deposition instead of etching occurred by mixing more than 6%. Therefore, by mixing 3–4% of C4F8 to BCl3, infinite etch selectivity of ZrO x /Si could be obtained while maintaining the similar ZrO x etch rate. The differences in the etch behaviors of ZrO x and Si were related to the different thickness of C–F polymer formed on the surfaces. The thickness of the C–F polymer on the ZrO x surface was smaller due to the removal of carbon incident on the surface by forming CO x with oxygen in ZrO x . Using 12 mTorr BCl3/C4F8 (4%), 700 W of rf power, and − 80 V of dc bias voltage, the ZrO x etch rate of about 535 Å/min could be obtained with infinite etch selectivity to Si.
Keywords: ZrO x selective etching; BCl3; C4F8;

Phase transition characteristics of Bi/Sn doped Ge2Sb2Te5thin film for PRAM application by Tae-Jin Park; Se-Young Choi; Myung-Jin Kang (5049-5053).
The Bi and Sn were doped to Ge2Sb2Te5 (GST) to investigate and modify the phase transition characteristics. The Bi/Sn doped GST thin film was prepared by RF magnetron co-sputtering and its crystal structure, sheet resistance, and phase transition kinetics were analyzed. By the doping of Bi/Sn, the crystallization temperature or stable phase was changed slightly compared with GST. For the PRAM application, the optimum doping concentration was Bi 5.9 and Sn 17.7 at.%, and its minimum time for crystallization was shorten more than 30% compared with GST. The sheet resistance difference between amorphous and crystalline state was higher than 104 Ω/□.
Keywords: Chalcogenides; Physical vapor deposition (PVD); Crystallization; Electrical properties and measurements;

Formation of (001)-textured grain in (111) polycrystalline silicon film by Jae Hwan Oh; Eun Hyun Kim; Dong Han Kang; Jun hyuk Cheon; Kyung Ho Kim; Jin Jang (5054-5058).
We report the formation of (001)-textured gains in (111) polycrystalline silicon (poly-Si) by Ni-mediated crystallization of amorphous silicon (a-Si) using a cap layer (MICC). The a-Si precursor deposited by plasma enhanced chemical vapor deposition was dehydrogenated at 550 °C and then crystallized at 580 °C. The (001)-textured grains appear in the network of (111) poly-Si of ∼ 100 μm grains, which was confirmed by the analysis of electron back-scattered diffraction. From the kinetic study of the grain growth, it is found that the nucleation rate of (001) nuclei is higher than that of (111) ones, but the (111) grains grow faster than that of (001) grains.
Keywords: Crystallization; Polycrystalline silicon; Thin-film transistor;

Electromagnetic sources of nonuniformity in large area capacitive reactors by A.A. Howling; L. Sansonnens; Ch. Hollenstein (5059-5064).
Theory and experiment show that two electromagnetic modes are necessary and sufficient to determine the field nonuniformity within a parallel-plate rf capacitive plasma reactor. These two modes give rise to the standing wave effect and the telegraph effect. The standing wave effect is associated with high frequencies in large reactors where the reactor size is larger than about a tenth of the vacuum wavelength of the rf excitation. The telegraph effect is associated with asymmetric electrode areas, which necessitates the redistribution of rf current along the plasma to maintain rf current continuity.
Keywords: Electromagnetic uniformity; Capacitive reactor;

The electroplating of the gate electrode on a flexible polyimide (PI) substrate was successfully applied to the fabrication of inverted-staggered poly(3-hexylthiophene) (P3HT) organic thin film transistors (OTFTs). The Ni gate electrode was electroplated through patterned negative photo-resist (KMPR) masks onto Cu (seed)/Cr (adhesion) layers that had been sputter-deposited on O2-plasma-treated PI substrates. The electrical measurements of the fabricated OTFTs with the SiO2 gate insulator indicated non-ideal output characteristics, which are similar to the model of electrical transport by a space-charge limited current (SCLC). The use of a poly(4-vinyl phenol) (PVP) and SiO2/PVP bilayer gate dielectric produced output characteristics that were closer to the ideal TFT behavior but led to a lower effective mobility and on/off current (I on/I off).
Keywords: Organic thin film transistor; P3HT; Ni electroplating; Flexible devices;

Synthesis and blue electroluminescent properties of zinc (II) [2-(2-hydroxyphenyl)benzoxazole] by Won Sam Kim; Jung Min You; Burm-Jong Lee; Yoon-Ki Jang; Dong-Eun Kim; Young-Soo Kwon (5070-5074).
This study reports on the properties of organic light-emitting diodes (OLEDs) with zinc (II) [2-(2-hydroxyphenyl)benzoxazole] as a hole-blocking layer. OLEDs devices are prepared in a conventional OLEDs structure (i.e., anode/HTL/EL/HBL/cathode and anode/HTL/HBL/EL/cathode). The luminescence efficiencies and the turn-on voltage are significantly affected by the existence of the hole-blocking layer. This is attributed to an excellent hole-blocking property, which is in turn due to the high HOMO energy level (6.5 eV). The device showed luminous efficiency 2.46 lm/W at 5 V. The maximum luminance of about 10,000 cd/m2 is obtained, and the turn-on voltage (2.5 V) is affected by the existence of the hole-blocking layer.
Keywords: 2-(2-Hydroxyphenyl)benzoxazole; Electroluminescence; Hole-blocking layer;

White OLEDs based on novel emissive materials such as Zn(HPB)2 and Zn(HPB)q by Yoon-Ki Jang; Dong-Eun Kim; Won-Sam Kim; Byung-Sang Kim; Oh-Kwan Kwon; Burm-Jong Lee; Young-Soo Kwon (5075-5078).
Organic light emitting diodes (OLEDs) show a lot of advantages for display purposes. Because OLEDs provide white light emission with high efficiency and stability, it is desirable to apply OLEDs as an illumination light source and backlight in LCD displays. We synthesized new emissive materials, namely [2-(2-hydroxyphenyl)benzoxazole] (Zn(HPB)2) and [(2-(2-hydroxyphenyl)benzoxazole)(8-hydoxyquinoline)] (Zn(HPB)q), which have a low molecular compound and thermal stability. We studied white OLEDs using Zn(HPB)2 and Zn(HPB)q. The fundamental structures of the white OLEDs were ITO/PEDOT:PSS (23 nm)/NPB (40 nm)/Zn(HPB)2 (40 nm)/Zn(HPB)q (20, 30 or 40 nm)/Alq3 (10 nm)/LiAl (120 nm). As a result, when the thickness of the Zn(HPB)q layer was 20 nm, white emission is achieved. We obtained a maximum luminance of 15325 cd/m2 at a current density of 997 mA/cm2. The CIE (Commission International de l'Eclairage) coordinates are (0.28, 0.35) at an applied voltage of 9.75 V.
Keywords: White OLEDs; Zn(HPB)2; Zn(HPB)q; Cyclic-voltammetry;

In this study, Ir(III) complex with 4,6-diphenylquinazoline (DPQN) was designed and characterized theoretically. The Hartree–Fock (HF) method with the 3-21G(d) basis set and density functional theory (DFT) utilizing the B3LYP functional with the 6-31G(d) basis set were used for the geometry optimization and the energy level calculation of the ground state of these complexes, respectively. Excited triplet and singlet states are examined using the time-dependent density functional theory (TD-DFT). As a result, it was found that these complexes produced a deep red emission due to the elongated conjugation length. The Ir(III) complex with DPQN ligands exhibits the large emission efficiency and emits light of the deep red wavelength.
Keywords: Quinazoline; Ir complex; Phosphorescence;

The synthesis and photophysical study of efficient phosphorescent heteroleptic tris-cyclometalated iridium(III) complexes having two different (C^N) ligands are reported. In order to improve the luminescence efficiency by avoiding triplet–triplet (T–T) annihilation, new heteroleptic tris-cyclometalated iridium complexes, Ir(ppy)2(dpq), Ir(ppy)2(dpq-3-F) and Ir(ppy)2(dpq-CF3), are designed and prepared where ppy, dpq, dpq-3-F and dpq-CF3 represent 2-phenylpyridine, 2,4-diphenylquinoline, 2-(3-fluorophenyl)-4-phenylquinoline, and 4-phenyl-2-(4-(trifluoromethyl)phenyl)quinoline, respectively. Ppy ligands and dpq derivatives can act as a source of energy supply. When new heteroleptic tris-cyclometalated iridium complex, Ir(ppy)2(dpq-3-F) is placed in the lowest excited state, the excitation energy is neither quenched nor deactivated but quickly intermolecularly transferred from two ppy ligands to one luminescent dpq-3-F ligand. Such transfer can occur because the triplet energy level of Ir(ppy)3 is higher than that of Ir(dpq-3-F)3 and because Ir(dpq-3-F)3 was known to have a shorter lifetime than that of Ir(ppy)3. As a result, Ir(ppy)2(dpq-3-F) shows strong emission band at 620 nm from dpq-3-F ligand in the end. Thus it allows more reddish luminescent color and improves the luminescence by the decrease of quenching or energy deactivation by decreasing the number of the luminescent ligand. To analyze luminescent mechanism, we calculated these complexes theoretically by using computational method.
Keywords: Ir(ppy)2(dpq); Ir(ppy)2(dpq-3-F); Red phosphorescence;

Ir(β) complexes of fluorinated dpqs(dpq-3-F, dpq-4-CF3) as a cyclometallated ligand were prepared and their photonic properties were investigated, where dpq-3-F and dpq-4-CF3 represent 2-(3-fluoro-phenyl)-4-phenylquinoline and 4-phenyl-2-(4-trifluoromethylphenyl)quinoline, respectively. Fluorinated dpq derivatives were introduced to the iridium complexes to increase the efficiency compared to Ir(dpq)2(acac) which was recently reported to have emission wavelength of 614 nm with quantum efficiency of 0.14. These fluorinated ligands and their Ir(III) complexes were computationally calculated by ab initio methods to support our experimental results. It was found that the Ir complex containing dpq-3-F ligands exhibits the largest emission efficiency with maximum emission peak at 593.5 nm. The result of ab initio calculation using the time-dependent density functional theory (TD-DFT) showed that the strong 3MLCT transition of the complex occurs due to the strong coupling between the 5d orbital of the Ir atom and the highest occupied molecular orbitals (HOMOs) of these ligands.
Keywords: Fluorinated dpq ligands; Ir complex; Red phosphorescence; DFT; OLED;

The electrical and the optical properties of organic light-emitting devices (OLEDs) with a mixed layer acting as a hole transport layer and as an emitting layer/electron transport layer were investigated. The OLEDs with a mixed layer showed the highest efficiency, and the emitting color of the OLEDs was pure yellow. The enhancement of the luminous efficiency in the OLEDs with a mixed layer was attributed to a decrease in hole mobility.
Keywords: Organic light-emitting diodes; Electrical properties; Optical properties; A mixed layer;

The electrical and the optical properties of organic light-emitting diodes (OLEDs) fabricated utilizing nickel-oxide (NiO) buffer layers between the anodes and the hole transport layers were investigated. The NiO layer was formed by using a thermally evaporated nickel thin film and a subsequent oxidation process. The tunneling holes in the OLED were increased due to the existence of the NiO layer between the anode and the hole transport layer, resulting in enhanced efficiency for the OLED. These results indicate that OLEDs with NiO buffer layers hold promise for potential applications in highly-efficient flat-panel displays.
Keywords: Organic light-emitting diodes; Electrical properties; Optical properties; Nickel oxide;

Optical and electrical properties of p-type transparent conducting CuAlO2 thin film by D.S. Kim; S.J. Park; E.K. Jeong; H.K. Lee; S.Y. Choi (5103-5108).
P-type transparent conducting CuAlO2 thin films were prepared by e-beam evaporation and wet-oxidation technique. CuAlO2 film was preferentially (006) oriented after wet-oxidation. The transmittance varied from 20 to 85% and the resistivity varied from 5 × 10− 3 to 4 Ω cm with wet-oxidation conditions. The nature of p-type films was confirmed by the positive hall coefficient. Optical band gap was estimated to be in the range of 3.96–4.20 eV. These behaviors were due to the decrease of oxygen deficient state in the film as oxidation progresses. Microstructural observations of films showed smooth morphology with 23.2–29.7 Å rms roughness.
Keywords: Oxidation; Optical properties; Resistivity; Electrical properties and measurements;

HfO2 gate insulator formed by atomic layer deposition for thin-film-transistors by S.-W. Jeong; H.J. Lee; K.S. Kim; M.T. You; Y. Roh; T. Noguchi; W. Xianyu; J. Jung (5109-5112).
We have investigated the effects of annealing temperature on the physical and electrical properties of the HfO2 film deposited by an atomic layer deposition (ALD) method for high-k gate oxides in thin-film-transistors (TFTs). The ALD deposition of HfO2 directly on the Si substrate at 300 °C results in the formation of thin HfSi x O y interfacial layer between Si and HfO2. The subsequent low temperature N2-annealing of HfO2 films (i.e., 300 °C) using a rapid thermal processor (RTP) improves the overall electrical characteristics of HfSi x O y –HfO2 films. Based on the current work, we suggest that HfO2 film deposited by the ALD method is suitable for high-k gate oxides in TFTs, which have to be fabricated at low temperature.
Keywords: Thin-film-transistor; ALD; High-k oxide; HfO2;

In order to improve the discharge characteristics of MgO protective layer, SiO2 was added to MgO thin films. The MgO–SiO2 thin films were deposited by electron beam evaporation method. The crystallinity and surface roughness of thin films were determined by XRD and AFM. Discharge characteristics of MgO–SiO2 protective layers were observed by changes in discharging voltages and SEE and memory coefficients as a function of Si concentration in the protective layer. The discharge characteristics of MgO–SiO2 layer were mainly affected by changes in crystallinity and surface roughness of films with Si concentration in the range of present study. With addition of 12.5 Si at.% in MgO–SiO2 protective layer, the discharge voltages and memory and SEE coefficients were considerably improved in comparison to pure MgO protective layer.
Keywords: Plasma display panel; MgO–SiO2 protective layer; Crystallinity; Surface roughness; Discharge characteristics;

Wall charge characteristics in accordance with square and ramped reset pulse in alternating current plasma display panels (AC-PDPs) by S.B. Lee; J.H. Lee; H.J. Lee; M.W. Moon; P.Y. Oh; K.B. Song; E.H. Choi (5118-5122).
The characteristics of wall charge after squared and ramped reset pulse have been experimentally investigated in an AC-PDP with a versatile driving simulator (VDS) system, in which arbitrary driving waveforms and sequences can be edited. Rising or falling times of ramped reset pulse have been varied to be 0, 30, 70, 110 and 150 V under fixed zero falling or rising times, respectively, and the reset voltage is fixed to be 320 V. The longer rising (either falling) times under zero falling (either rising) time in reset pulse make the less IR intensity caused by weak self-discharge that occurred at falling (either rising) time in reset pulse. Generally, the ramped reset pulses have been observed to have large wall voltages of 100 to 200 V while the squared reset pulses are to be 4 V by the weak self-discharges at falling time of reset pulse in this experiment.
Keywords: Alternating current plasma display panel; Wall charge; Wall voltage; Reset pulse;

One-dimensional carbon and ZnO by J.M. Ting; K.H. Liao; T.L. Chou (5123-5130).
Carbon nanotube (CNT) and one-dimensional ZnO are two of the most important nano materials for which continuous efforts are being made for the development of novel processes. In this paper we present new approaches for the growth of CNTs and ZnO nanorods. Through the selection of an appropriate catalyst, namely, Fe–Si thin film, aligned CNT can be obtained at a temperature as low as 370 °C using a conventional microwave plasma-enhanced chemical vapor deposition (MPCVD) technique. This is attributed to the fact that the addition of Si greatly enhances the carbon diffusion such that a fast reaction-controlled growth is obtained. Also, with the use of a decisive electroless copper layer deposited on Si or glass substrate, semi-aligned ZnO nanorods can be obtained at the room temperature. It was found that the residual stress in the electroless copper is the key to the formation of ZnO nanorods.
Keywords: CNT; Catalyst; ZnO nanorods; Electroless copper; Growth;

Fabrication of dye sensitized solar cell using TiO2 coated carbon nanotubes by Tae Young Lee; P.S. Alegaonkar; Ji-Beom Yoo (5131-5135).
We fabricated a dye sensitized solar cells (DSCs) using TiO2 coated multi-wall carbon nanotubes (TiO2-CNTs). Carbon nanotubes (CNTs) have excellent electrical conductivity and good chemical stability. We introduced CNTs in DSCs to improve solar cell performance through reduction of series resistance. TiO2-CNTs were obtained by Sol–Gel method. Compared with a conventional TiO2 cell, the TiO2-CNTs content (0.1 wt.%) cell showed ∼ 50% increase in conversion efficiency, which is attributed to the increase in short circuit current density (J sc). The enhancement in J sc occurs due to improvement in interconnectivity between the TiO2 particles and the TiO2-CNTs in the porous TiO2 film.
Keywords: Dye sensitized; Carbon nanotubes; Passivation layer;

Mechanical properties of electrospun PVA/MWNTs composite nanofibers by J.S. Jeong; J.S. Moon; S.Y. Jeon; J.H. Park; P.S. Alegaonkar; J.B. Yoo (5136-5141).
Composites of polyvinyl alcohol (PVA) and multi-walled carbon nanotubes (MWNTs) were prepared by electrospinning. A PVA/MWNTs solution was electrostatically spun to form filler wrapped nanofibers, with a diameter of ∼ 100–200 nm. As the concentration of filler in the composite was varied, the coloration of the fiber sheets changed. The SEM and TEM analyses of the fiber sheets revealed that the deformation of the fiber increases with increasing nanotube concentration. The mechanical properties were studied using a universal testing machine (UTM). The analysis is presented in detail. It is argued that the degree of dispersivity orientation and anisotropy of the nanotubes and the amount of interfacial stress in the filler/polymer are the predominant factors determining the variation in the tensile properties of the composites with the filler concentration.
Keywords: Electrospinning; Nanofibers; MWNTs; PVA;

Diamond-like amorphous carbon (DAC) films were deposited for field-emission application using supermagnetron plasma by mixing N2 or H2 in i-C4H10 gas at the upper and lower electrode rf powers (UPRF/LORF) of 800 W/100–800 W. At an 800 W/800 W, the N2 (0–80%) gas-mixed DAC films showed an emission threshold electric field (E TH) of 19 V/μm. At the 800 W/100 W, the H2 (20%) gas-mixed DAC film showed low E TH's of 13 V/μm, respectively. The moderate reduction of CC and CN double bonds by the decrease of LORF from 800 W to 100 W was found to be effective to lower E TH.
Keywords: Diamond-like amorphous carbon; Field emission; Chemical vapor deposition; Supermagnetron plasma;

Nanostructures less than 200 nm in size are created by the Fresnel diffraction of 157 nm light at the aperture margins of a photomask through proximity irradiation of an octadecyltrimethoxysilane self-assembled monolayer. Photochemical decomposition of the organic monolayer creates complex nanostructure patterns, according to the light intensity distribution at the substrate location. Dimensions and distribution of the nanostructures correlate well with the spatial distribution of the light intensity calculated using the Fresnel equations.
Keywords: Self-assembled monolayers; Fluorine laser; Proximity lithography; Diffraction patterns;

Realization of various sub-micron metal patterns using room temperature nanoimprint lithography by Jun-Ho Sung; Min-Woo Lee; Seung-Gol Lee; Se-Guen Park; El-Hang Lee; Beom-Hoan O (5153-5157).
Nanoimprint lithography (RT-NIL) process using hydrogen silsesquioxane (HSQ) provides a simple fabrication method to realize sub-micron-sized patterns because it can be applied at room temperature. When the process is performed on a HSQ–PMMA bi-layer resist, it is suitable to additional metal sputtering and lift-off process because it features negative vertical profiles. However, high viscosity of HSQ at room temperature requires a high imprint pressure, and also limits the applicable mold profile. Thus, the HSQ imprint depth dependencies on prebaking temperature and mold protrusions are investigated and results are analyzed using the equations for squeezed flow of polymers which enable us to predict typical imprint results under specific conditions. Based on these investigations, the RT-NIL process was optimized and, then, various sub-micron-sized metal patterns of line and hole array were fabricated.
Keywords: Nanoimprint lithography; Hydrogen silsesquioxane; Bi-layer resist;

Bicrystalline gallium oxide nanobelts by Hyoun Woo Kim; Seung Hyun Shim (5158-5162).
We have synthesized gallium oxide (Ga2O3) nanobelts by heating GaN powders in the conventional furnace. The nanobelts exhibited a unique bicrystalline structure that consisted of two single-crystalline monoclinic Ga2O3 nanobelts, which split along the twin boundary that exists at the centerline. Energy dispersive X-ray spectroscopy and electron energy loss spectroscopy spectra coincidentally indicated the presence of nitrogen in the Ga2O3 nanobelts. Photoluminescence spectra exhibited the visible light emission. We discussed the possible emission mechanisms, including the effect of the nitrogen dopant.
Keywords: Bicrystalline; Ga2O3; Nanobelts;

Study on electrical conduction of viologen derivatives using scanning tunneling microscopy by Nam-Suk Lee; Hoon-Kyu Shin; Dong-Jin Qian; Young-Soo Kwon (5163-5166).
The electrical conduction of self-assembled monolayers (SAMs) made from viologen derivatives was measured using ultrahigh vacuum scanning tunneling microscopy (UHV-STM) with a focus on the molecular structural effect on the electrical conduction. For viologen derivative SAMs, resistances through the monolayers increased exponentially with increases in molecular length when the decay constants of transconductance β were ca. 0.35 to 0.48 nm− 1. The estimated monolayer resistances of the viologen derivatives such as N-methyl-N′-(10-mercaptodecyl)-4,4′-bipyridinium (VC10SH), N-methyl-N′-di(8-mercaptooctyl)-4,4′-bipyridinium (HSC8VC8SH), and N-methyl-N′-di(10-mercaptodecyl)-4,4′-bipyridinium (HSC10VC10SH) SAMs were 1.3 × 108 Ω, 3.6 × 109 Ω, and 3.8 × 109 Ω, respectively.
Keywords: Ultrahigh Vacuum Scanning Tunneling Microscopy (UHV-STM); Viologen derivatives; Self-Assembled Monolayers (SAMs);

Fabrication of nano-pillar chips by a plasma etching technique for fast DNA separation by R. Ogawa; H. Ogawa; A. Oki; S. Hashioka; Y. Horiike (5167-5171).
The fabrication of quartz nano-pillars was investigated using dry etching with a Ni mask. The mask diameter increased during etching due to re-sputtering of the Pt/Cr seed layer. However, once the seed layer had been eroded the enlarged mask diameter did not increase any further. Hence, the use of the mask enabled the fabrication of nano-pillars with a high aspect ratio. In situ FTIR–ATR observation of HF quartz plate pressure bonding developed a new bonding technique involving the use of H2SiF6. The nano-pillar chips allowed then to size-separate DNA of 10 kbp and 38 kbp within 20 s.
Keywords: Nano-pillars; Quartz bonding; DNA electrophoresis; DNA size separation;

A scanning radical microjet (SRMJ) equipment using oxygen microplasma has been developed and successfully applied for controlling biological cells’ attachment on biocompatible polymer material, poly(dimethylsiloxane) (PDMS). The radical microjet has advantages in localized and high-rate surface treatment. Moreover, maskless hydrophilic patterning using SRMJ has been demonstrated to be applicable to patterned cell cultivation which is useful in emerging biotechnological field such as tissue engineering and cell-based biosensors. Since control of PDMS surface properties is an indispensable prerequisite for cells’ attachment, effects of oxygen flow rates and treatment time on localized hydrophilic patterning of PDMS surfaces were first investigated for controlling HeLa cells’ (human epitheloid carcinoma cell line) attachment. Relationships between surface conditions of treated PDMS films and attached cell density are also discussed based on surface properties analyzed using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS).
Keywords: Scanning radical microjet equipment; Poly(dimethylsiloxane) (PDMS); Surface modifications; Cell adhesion;

Amperometric biosensor based on direct electrochemistry of hemoglobin in poly-allylamine (PAA) film by A.K.M. Kafi; Dong-Yun Lee; Sang-Hyun Park; Young-Soo Kwon (5179-5183).
Hemoglobin (Hb) was immobilized in poly-allylamine (PAA) film onto the gold electrode by layer by layer (LBL) method. The modified electrode exhibited a pair of well-defined peaks during cyclic voltammetry, which was attributed from the direct electron transfer of heme proteins. The immobilized Hb showed an excellent electrocatalytical response to the reduction of hydrogen peroxide. The sensor exhibited a fast response and high sensitivity. Through the use of optimized conditions, the linear range for H2O2 detection was from 2.5 × 10− 6 M to 5 × 10− 4 M with detection limit of 0.2 μM. The proposed biosensor showed long-lasting stability and excellent reproducibility.
Keywords: Hemoglobin; Poly-allylamine; Electrochemistry; Biosensor;

Controlled drug release using nanoporous anodic aluminum oxide on stent by Ho-Jae Kang; Deug Joong Kim; Sung-Joon Park; Ji-Beom Yoo; Y.S. Ryu (5184-5187).
Local drug delivery system was demonstrated by using drug-eluting stents coated with nanoporous anodic aluminum oxide (AAO) for controlled drug release. 316 stainless steel coronary stents were coated with nanoporous AAO, which was fabricated by anodization of Al deposited on stents. Effects of diameter and depth of AAO on the release of drug were investigated. Image of the AAO pore diameter and depth were examined by SEM. Amount of the drug release from the AAO with various pore diameters and depths was analyzed by HPLC.
Keywords: Anodic aluminum oxide; Drug release characteristics; Drug-eluting system;

Time evolution of non-uniform voltage distribution on the powered electrode in a large-area very-high-frequency (VHF) capacitively coupled plasma processing system is studied based on a one-dimensional transmission-line model with an equivalent-circuit model of the plasma. With this model, time evolution of voltage and current distributions on the electrode is examined at its activation by the power supply with various frequencies, waveforms, and power-supply locations. It has been found, with the power supply of multiple frequencies, that effects of beat waves can significantly affect plasma uniformity especially if the difference in frequency is small. It has been also demonstrated that, with multiple power-supply locations combined with multiple frequencies, good voltage uniformity over the long electrode can be obtained.
Keywords: Capacitively coupled plasmas; VHF; Standing wave; Transmission-line model;

A novel internal-type linear inductive antenna, referred to as a “double comb-type antenna”, was used as a large-area plasma source with a substrate area of 880 mm × 660 mm. This study investigated the effect of a multi-polar magnetic field on plasma confinement. High density plasma in the order of 3.2 × 1011 cm− 3, which is 50% higher than that obtained for a source without a magnetic field, with good plasma stability was obtained at a pressure of 15 mTorr Ar and an RF power of 5000 W. Plasma uniformity < 3% within the substrate area was also obtained.
Keywords: ICP; Large-area; Display; Magnetic confinement;

A new DC plasmatron with a hot rod cathode and cold nozzle anode was proposed and tested at atmospheric pressure, generating nearly spectrally clean plasmas of air, air/diesel fuel mixture, oxygen, and CF4. The arc Volt–Ampere characteristic (VAC) is an integral indicator reflecting the general behavior of all the arc parts, among which the most important are the by-electrode layers and positive column. The sensitivity of the VAC to the gas flow velocity in the technologic channel confirmed the external vortex nature of the anode arc spot, which does not hide inside the anode orifice, but exits it and interacts with the gas flow.
Keywords: Volt–Ampere characteristics; Plasmatron; Anode orifice;